Hitherto, the net posts used in volleyball and tennis, and the sports posts for soccer, rugby, American football and athletics, etc, have been made of iron or stainless steel metal. In the case of net posts in particular, in order to counter the bending moment generated when tension is applied to the net wire, the main structural parts have been made of fairly thick-walled metal from the point of view of strength. Further, the general extension/retraction mechanism in such posts is usually a system in which two or more hollow tubes are connected by fitting together telescopically, with the inner tube(s) being raised or lowered by means of a screw mechanism. With this extension/retraction mechanism, when an operating handle is introduced into an insertion hole provided in the outer tube side face and a built-in bolt rotated via a bevel gear, the inner tube to which a nut is fixed is raised and, in this way, adjustment is possible to the appropriate net height for each sporting event. When rotating the bolt, it is necessary to prevent co-rotation of the nut portion. In conventional steel posts, a lead-in groove is cut in the surface of the inner tube to which the nut is fixed, running in the axial direction of the tube. A key provided in the outer tube engages this lead-in groove. In this way, it is possible to raise and lower the inner tube without co-rotation occurring along with the rotation of the bolt.
Conventional thick-walled metal sports posts are extremely heavy, and considerable physical effort is required in their setting up and taking down. For example, taking the case of net posts, which are one type of sports posts, when these are employed in a multi-purpose location such as a gymnasium, unlike in a dedicated court, the posts have to be frequently set up and taken down, and where the net posts are long and, consequently, heavy, like the posts for volleyball, their setting up and taking down is accompanied by physical strain on the part of the user.